1. Field of the Invention
The present invention relates generally to the treatment of bone fractures or abnormal bone conditions which require osteotomies, and more particularly to an intramedullary rod system for stabilizing bone segments.
2. Description of Prior Art
The fracture of certain bones, such as the femur, tibia, ulna, radius and humerous, requires substantial immobilization of the fractured bone sections in an abutting relationship during the healing process. Any longitudinal, transverse, or rotational movement of one fractured bone section relative to the other may cause a substantial delay in healing time or improper healing of the bone itself. In general, prior art provides various internal fixation approaches that have been used to immobilize the area surrounding the fracture site.
One approach involves driving metallic pins through the two sections of bone to be joined and connecting them to one or more plates bearing against the external surface of the bones. However, such an arrangement may cause injury to the surrounding outer layer and decrease blood supply and delay or inhibit bone healing. Plates also tend to shield the bone from stress and decrease the strength of the underlying bone.
Another approach for treating fractures involves the use of an intramedullary nail or rod which is inserted into the medullary canal of the bone, so as to be affixed therein. After complete healing of the bone at the fracture site, the rod may be removed through a hole drilled in the proximal or distal end of the bone.
A prior art flexible intramedullary nailing technique for affixing and mobilizing bone segments is illustrated in FIG. 1. This technique includes drilling oblique lateral and medial openings 12, 14 in the fractured bone 10 above the physis 16, then inserting pre-bent flexible stainless steel or titanium nails 18 and 20 (shown in dashed line), which are typically 2-4 mm in diameter, into the bone interior or canal 22 through the openings in a retrograde manner. Prior to insertion, each nail 18, 20 must be bent or curved such that their apexes 24, 26 are at the level of the fracture 25. Since the fracture may be oblique to a central axis of the bone as shown in FIG. 1, the nails 18, 20 may be bent at different locations. Using fluoroscopy to visualize rod progression and placement, the nails are advanced through the bone until they cross the fracture. The nails are then cut to length. Distal ends 28 and 30 of the nails are left extending slightly into the soft tissue surrounding the bone 10.
Although flexible nails have been utilized by some doctors (primarily in pediatric patients with small diameter long bones), there are drawbacks to their use. For instance, the nails are not securely fixed within the intra medullary canal. Moreover, flexible nails lack the rotational stability of rigid nails and normally cannot be used in highly unstable or comminuted fractures.
FIG. 2 depicts another prior art solution that makes use of a flexible rod 32 (shown in dashed line). The rod 32 is inserted into the medullary canal 22 of the tibia 10. The rod 32 is inserted manually as far as possible. An image intensifier is used to locate the distal end 34 of the rod. The proximal end 36 of the rod is then bent over in an attempt to anchor the rod to the bone area. The distal end 34 may be left unanchored to allow for growth of the bone, resulting in unpredictable positioning of the rod. Alternatively, the distal end 34 may also be bent over and fixedly attached to the distal end of the bone, but is nevertheless haphazard and imprecise.
FIGS. 3 and 4 show another prior art solution involving an unreamed tibial nail 40 (shown in dashed line). The nail 40 is inserted into the medullary canal 22 of the tibia 10, medial to the patellar tendon and as superior as possible. The nail 40 includes a plurality of openings 42 for receiving screws 44. Once in position, the location of the openings 42 are determined by fluoroscopy and the screws 44 are inserted transversely through the bone and openings 42 for anchoring the nail 40 in place. Although this type of system may be acceptable for bones having relatively large cross sections, it is difficult to implement in smaller bone structures due to size restraints. This is especially typical pediatric cases. For example, a typical nail may have a diameter in the range of 8-9 mm and the screws may have a thread diameter of approximately 4 mm in order to properly secure the nail to the bone. For pediatric situations or other cases where it may be impractical to insert a large diameter nail into a small bone, a suitable nail may have a diameter in the range of 2-4 mm and thus would require a screw with a substantially smaller thread diameter. However, forming a hole in the 2-4 mm nail would be quite difficult, and the provision of a substantially smaller screw to fit in the hole would not provide sufficient cross-pinning to isolate movement of the nail or to fix it in a desired position.